Infrequently Asked Questions: Why do we fall asleep so easily during car rides?

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Car rides are a reliable trick for getting fussy kids to fall asleep, but it seems to work pretty well on adults, too, Why is that? Is it the movement, the noise, the close quarters?

Let’s say we’re riding in a car as a kid or an adult. Why is it that it’s usually a little easier to get to sleep?

I think there are several reasons. It depends on whether we’re talking about adults or children, but let’s talk about it as a general thing. It’s probably because we are sedentary. So, it may or may not be the movement, but certainly just being sedentary and not having all those other things to busy our minds. Once you’re in the car you're strapped in, not running around and, if you’re tired, no matter how much sleep you got the night before ... when you run around all day, you really can’t fall asleep because you’re on your feet. But when you’re sedentary, suddenly you're strapped in a car, you can’t go anywhere, you might be looking at pretty things around you and you don’t think about all the stresses at work or home and all that.

The purring of the car and all that takes your mind off that and you fall asleep. If you're really well-rested, of course, you’re not going to fall asleep.

How much of it do you think is the white noise?

I think white noise is part of it, because once you’re on the highway there’s that general hum the car has, if you don’t have a lot of honking going on. If you’re on the turnpike and cruising along there is that white noise — the hum of the tires on the road — and a lot of people fall asleep to that white noise.

And then there's some thought that for some people it also is sort of womb-like. You’re in this car and protected and warm and cozy. That womb-like thing that perhaps comes back, if you believe in the psychological reasons of how you fall asleep. If you feel comfortable with the person who’s driving — especially a kid, who’s always comfortable with their parents driving — then there’s the womb-like effect and they may fall asleep. And I think little kids may fall asleep easier if they were rocked as a baby. So, babies who get rocked to sleep — which is always a bad idea, but we do it anyway — if you rock them to sleep and then they’re in the car, and they’re rocked by the motion, they may fall asleep ...

Is that a psychological thing? Doesn't sound like it's the movement.

Yes. It’s just associated with, ‘If I get rocked, I fall asleep.’ There are babies who, if you rock them to sleep, then they need to be rocked to sleep, and then every time you rock them they’re going to fall asleep by association. I don’t think it’s the movement, per se; I just think it’s cozy, a good temperature and you can’t do anything else, and we’re all so sleep-deprived that it allows us to fall asleep. But I don’t know any science that shows it’s the movement itself — certainly, if there is a lot of movement, you can’t fall asleep. If you ride a roller coaster you can’t fall asleep.

Kids don’t normally think about whether a good driver is at the wheel. Maybe that’s why they sleep more during rides?

I do think that’s true –— I don’t know science that's shown that, but I do think that’s true. I mean, I definitely can’t fall asleep with certain people driving, but with others, I might be able to. So if I’m on a train and I trust the conductor, I may fall asleep, whereas if I’m driving with someone I don’t know that well I’m definitely not going to fall asleep, because I don’t know if they’re a good driver.

But a lot of it, as adults, is we’re all sleep-deprived. So as soon as we’re warm, cozy, have a seatbelt on and the temperature is right, with a little white noise — boom. We’re tired anyway. We could fall asleep at any point during the day because most of us don’t get enough sleep.

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